1. Field of the Invention
This invention relates to a dehydrating purification process for a fermentation product, more particularly to a purification process for producing Sophorolipid or a secondary derivative thereof having a lower viscosity, which comprises purifying by dehydration Sophorolipid or a secondary derivative thereof which is a fermentation product of Torulopsis bombicola.
2. Description of the Prior Art
It has been reported by J. F. T. Spencer et al. [Canadian Journal of Chemistry, 39, 846 (1961)] that a great quantity of Sophorolipid is produced in a fermentation liquid by culturing Torulopsis bombicola.
Sophorolipid is considered to be a mixture of the compounds represented by the formulae (I) and (II), ##STR2## wherein R.sub.3 represents a hydrogen atom or a methyl group, and R.sub.4 represents a saturated or unsaturated hydrocarbon group having 12 to 16 carbon atoms when R.sub.3 is a hydrogen atom, and R.sub.4 represents a saturated or unsaturated hydrocarbon group having 11 to 15 carbon atoms when R.sub.3 is a methyl group.
These compounds are useful as cleansers and emulsifiers having both excellent hygroscopic and hydrophilic properties due to their Sophorose groups and hydrophobic properties arising from the fatty acid. Particularly, the hygroscopic property due to the Sophorose group and the cleansing ability arising from the fatty acid provide a wetting agent with excellent properties which in addition support skin physiology.
However, Sophorolipid is an aggregate of many homologs. For instance, when fermented with an octadecane as a source of hydrocarbon, there is produced about 40% of (I-a), about 8% of (I-b) and (I-c), about 30% of (II-a), about 6% of (II-b) and (II-c), about 14% of an isomer resulting from the position of the lactone bond, and small amount of (I-d) and (II-d). The formation ratio of these homologs varies depending on the hydrocarbon source and fermentation conditions.
As can be seen from the above structures, the compounds of the formula (I) differ from those of the formula (II) in the bonding of the fatty acid moiety. Consequently, the number of hydroxy groups in the Sophorose group and the acetyl values of the homologs are different from each other. These structural differences result in diversified physicochemical properties. Namely, the solubility in organic solvents and water and the surface-active properties vary, depending on the structure. For instance, the compound of the formula (I-a) possesses an oily property, and is readily soluble in water, and the compounds of the formulae (I-b) and (I-c) have emulsifying characteristics to some extent. The compound of the formula (I-d) is readily soluble in water and has a cleansing ability with a rather high HLB value. The compound of the formula (II-a) is emulsified and dispersed in water and acts as an excellent emulsifier. The compounds of the formulae (II-b) and (II-c) are readily soluble in water and possess a cleansing ability and foaming properties. The compound of the formula (II-d) remarkably functions as a cleanser having an HLB value of 30 to 40, which value is not less than those of anionic surface active and a non-ionic cleansers.
Therefore, it should be noted that the properties and functions vary with the ratios of those homologs because the mixture of the homologs is actually used. Further, difficulty is encountered in that a desired product having a given ratio of the homologs must be produced by fermentation.
The acetyl and lactone bonds in Sophorolipid are chemically unstable and easily cleaved under weakly alkaline conditions (pH 9-10) at room temperature. This cleavage is promoted also under mineral acid conditions. Even in the vicinity of neutrality, both bonds are gradually hydrolyzed by heating or during prolonged storage of Sophorolipid so that Sophorolipid is finally converted into the compound of the formula (II-d).
However, the principal carbon skeleton of Sophorolipid is a L-[(2'-O-.beta.-D-glucopyranosyl-.beta.-D-glucopyranosyl)-oxy]alkane acid or alkene acid which is formed by combining Sophorose with a hydroxyfatty acid via a glycosyl ether bond and is chemically stable.
Consequently, various secondary derivatives of Sophorolipid have been produced which are of good and stable quality and performance. Some typical compounds of these derivatives are as follows: ##STR3## wherein R.sub.5 represents a hydrogen atom or a methyl group, R.sub.6 represents an alkyl group having 2 to 20 carbon atoms, R.sub.7 represents a hydroxyalkyl group having 2 to 5 carbon atoms, and R.sub.3 and R.sub.4 are the same as defined above.
These secondary derivatives are stable and have surmounted the above noted defects. However, the production of these derivatives involves various problems. That is, only Sophorolipid having a water content of 40 to 50% is obtained from the fermentation liquid by decantation. The existence of water inhibits the reaction, prevents Sophorolipid from conversion into secondary derivatives and causes by-products. For instance, when Sophorolipid is subjected to a methanolysis reaction with an acid catalyst in the presence of water in order to obtain the compound of the formula (V), only a mixture of the compounds of the formulae (V) and (II-d) is produced, and no single substance can be obtained.
With the exception of ethyl acetate, there have been found no solvents which can extract Sophorolipid efficiently from a Sophorolipid solution obtained from the fermentation liquid or by any slant method because Sophorolipid is an aggregate of many homologs which are very different in their solubilities in organic solvents.
Ethyl acetate allows for the recovery of at most 80% but is indispensably coexistent with water by reason of the fact that ethyl acetate itself contains 5 to 10% of water. Even if the existing water is eliminated with a dehydrating agent, the secondary derivatives cannot be prepared in an ethyl acetate solvent system since the solvent itself acts as a reacting substrate. Therefore, the solvent must be exhaustively distilled off.
However, exhaustive elimination of the water or solvent is nearly impossible from an industrial standpoint because Sophorolipid and secondary derivatives thereof are extremely viscous substances as shown in Table 1.
Table 1 __________________________________________________________________________ Viscosity of Sophorolipid and secondary derivatives thereof Sophorolipid Secondary derivatives (.degree.C.)Temperature 14.1%contentWater 5.3%contentWater 0.4%contentWater (II - d)Compound (R.sub.5 = CH.sub.3)(V)Compound (R.sub.6 = C.sub.18 H.sub.35)(VI)Compo und ##STR4## __________________________________________________________________________ 20 &gt;100,000 &gt;100,000 &gt;100,000 &gt;100,000 &gt;100,000 &gt;100,000 &gt;100,000 60 320 1,900 (65.degree. C.) &gt;100,000 &gt;100,000 &gt;100,000 4,300 63,000 80 150 1,350 20,000 &gt;100,000 38,000 12,000 1,400 __________________________________________________________________________ Note: The numerical values indicate viscosities (cps) measured with a B type viscosimeter made by Tokyo Keiki Co., Ltd.
In view of these difficulties, the present inventors have made continued studies on the lowering of viscosities of Sophorolipid and secondary derivatives thereof. Substances to be added for this purpose should preferably have the following properties:
1. Good miscibility with Sophorolipid or secondary derivatives thereof.
2. Liquid form at room temperature.
3. Significant decrease in viscosity by addition of only a small amount.
4. Higher boiling point than water.
5. Not reactive or less reactive than reaction agents.
6. Do not interfere with the properties of a desired product even if reactive.
7. Safety to human bodies and others.
The present inventors have examined a wide variety of substances, and as a result, have found that polyhydric alcohols meet with the above desired properties and give the best results. Based on this finding, this invention has been accomplished.